1. Field of the Invention
The present invention relates to an optical recording method for recording information by holography, an optical recording apparatus using the method, an optical recording medium, an optical reproducing method, using the optical recording method. More specifically, the present invention relates to an optical recording method capable of effectively performing a location control for light irradiation, such as focusing control or tracking control, at the time of recording or reproducing, and efficiently performing adjustments related to thickness variations of a recording layer disposed in an optical recording layer or errors of an optical recording and reproducing apparatus, and the present invention relates to an optical recording apparatus, an optical recording medium, and an optical reproducing method using the method.
2. Description of the Related Art
An optical recording method for recording information on an optical recording medium by holography generally involves interference of information light (object light) having image information with reference light in an optical recording medium to record a resultant interference fringe on the optical recording medium. An example of such an optical recording method is a collinear strategy in which information light and reference light are collinearly applied. In this collinear strategy an interference fringe is formed as a result of interference between the information light and the reference light, recording image information or the like in its recording layers. The recorded information is reproduced by applying reference light identical to that for recording from the same direction to thereby produce diffracted light from the interference fringe and by receiving the diffracted light.
Upon recording or reproducing of image information or the like, controls of light focus points (e.g., focusing and tracking controls) are carried out for recording/reproducing information on/from a proper position of an optical recording medium, by adjusting variations in distance within a layer (e.g., recording layer) in the optical recording medium and/or variations in recording accuracy of the optical recording apparatus.
As a method for adjusting focus points, for example, a sampled servo method is available. In the sampled servo method, servo light is applied on an optical recording medium for focusing and tracking control, and reflected light is utilized to detect location information such as focusing information and/or tracking information for proper light irradiation. This method for adjusting focus points allows application of the information light and the reference light on the exact location on the optical recording medium, thereby recording or reproducing information (see Japanese Patent Application Laid-Open (JP-A) Nos. 2003-151143, 2003-178456 and 2003-228875).
However, on the aforementioned method for adjusting focus points, the detection is targeted only to the location information (e.g., the focusing information and the tracking information) of the servo light irradiation, and the applying location of the information light and the reference light in the thickness direction of the recording layer is not regarded as a target of the detection. Therefore, in the case where there is unevenness in the thickness of layers such as the recording layer or the position of the laminated layers relative to the thickness direction, or in the case where an error in the radiation of the optical recording and reproducing apparatus is occurred together with the error of the recording layer due to the unevenness of the thickness or layer positioning, the recording cannot be performed on the exact position even though the radiation position on the optical recording medium is controlled in advance. Especially when the recording layer is laminated with plural layers, as shown in FIG. 1, a production error is occurred between the designed distance Lw set in the optical recording and reproducing apparatus and the distance Mw of the actual optical recording medium, where the distance Lw is a designed distance from a surface of the first substrate 5 to the selective reflection layer (filter layer 6) which reflects the information light and the reference light in the optical recording medium, and the distance Mw is a distance from a surface of the first substrate 5 to the selective reflection layer (filter layer 6) in the actual optical recording medium. Similarly, an error is occurred between the designed distance Lg set in the optical recording and reproducing apparatus and the distance Mg in the actual optical recording medium, where the distance Lg is a designed distance from a surface of the first substrate 5 to the reflective layer 2 which reflects the servo light in the optical recording medium, and the distance Mg is a distance from a surface of the first substrate 5 to the reflective layer 2 in the actual optical recording medium.
Therefore, in the same optical recording and reproducing apparatus, even if the recording and reproducing can be properly performed on one optical recording medium, the reproducing may not be properly performed on another optical recording medium, and thus there is a problem in compatibility, such that the adjustment of the optical recording and reproducing apparatus is required. Since there is a limitation in reducing an error, such as unevenness of the layer thickness, during the manufacturing process, the manufacturing cost may be increased as a result of seeking such the highly accurate optical recording medium.
When recording is performed on such a good quality optical recording medium having no or only a little error, the detection of the focusing information, and the focusing control are generally performed only at the beginning, and once good quality of the optical recording medium is confirmed, the detection of the focusing information, and the focusing control are stopped. Thereafter, the address information, which is detectable even when a relatively large error exits, is detected, and then recording is performed based on the detected information. Therefore, the recording is properly performed with an accelerated recording speed.
When recording is performed on an optical recording medium having a large error, it is necessary to perform the detection of the focus information and focusing control per recording layer or recording region, or every recording, not only at the beginning, and thus the recording speed and recording efficiency are lowered.
Therefore, there are not yet realized an excellent optical recording method, optical recording apparatus, optical recording medium, and optical reproducing method, which are capable of effectively performing a location control for light irradiation, such as focusing control or tracking control, at the time of recording or reproducing, and efficiently performing adjustments related to thickness variations of a recording layer disposed in an optical recording layer or errors of an optical recording and reproducing apparatus. Accordingly, it is strongly desired to provide such that optical recording method, optical recording apparatus, optical recording medium, and optical reproducing method.